Although this invention is being disclosed in connection with cervical cancer, it is applicable to many other areas of medicine. Uterine cervical cancer is the second most common cancer in women worldwide, with nearly 500,000 new cases and over 270,000 deaths annually (http://wwwdepdb.iarc.fr/globocan2002.htm, incorporated herein by reference). Colposcopy is a diagnostic method used to detect cancer precursors and cancer of the uterine cervix (B. S. Apgar, Brotzman, G. L. and Spitzer, M., Colposcopy: Principles and Practice, W.B. Saunders Company: Philadelphia, 2002, incorporated herein by reference). Scoring schemes such as Reid's index are an aid for making colposcopic diagnoses (Reid R, Scalzi P. Genital warts and cervical cancer. VII. An improved colposcopic index for differentiating benign papillomaviral infection from high-grade cervical intraepithelial neoplasia. Am J Obstet Gynecol 1985; 153:611-618, incorporated herein by reference) based on various features, including acetowhitening, vessel patterns and lesion margins. These features are individually assessed and scored before the scores of all features are combined to yield a composite score that grades disease severity. However, the quality of the images must be assessed before further analysis, to ensure reliable scoring.
The limited quality of cervical imagery can be attributed to several factors, including: incorrect instrument settings, incorrect instrument positioning, glint, blur due to poor focus, and physical contaminants. Glint (specular reflection) eliminates the color information in affected pixels and can therefore introduce artifacts in feature extraction algorithms. Specular reflection is perfect, mirror-like reflection of light from a surface, in which light from a single incoming direction (a ray) is reflected into a single outgoing direction. A pixel is a single point in a graphic image and is the smallest single element of an image. Each pixel in an image has its own value that correlates to its brightness or intensity. In a color image, each pixel can be described using its hue, saturation, and value (HSV) or hue, saturation, lightness (HSL), but is usually represented instead as the red, green, and blue (RGB) intensities. Hue, saturation, and intensity (HSI) and hue, saturation, and brightness (HSB) are alternative names for HSV and HSL. HSL and HSV can be used to represent colors as points in a cylinder whose central axis ranges from black at the bottom to white at the top with neutral colors between them, where the angle around the axis corresponds to “hue”, distance from the axis corresponds to “saturation”, and distance along the axis corresponds to “lightness”, “value”, and “brightness”.
CAD for colposcopy represents a new application of medical image processing. The inventors have developed a CAD system that mimics diagnostic methods such as Reid's index in order to assess the severity of cervical abnormalities (Lange H. and Ferris, Daron G.; Computer-Aided-Diagnosis (CAD) for colposcopy; SPIE Medical Imaging 2005; SPIE Proc. 5747, 2005, incorporated herein by reference). In order to reliably assess colposcopic features, the imagery upon which CAD operates must be of high quality. Therefore, the present invention includes a systematic framework of algorithms called Active Image Quality Assessment (AIQA), which include locating a region of interest, contrast maximization, and composition analysis. These algorithms automatically assess cervical images acquired from a digital colposcope. The filtered dataset can then be used for CAD algorithms and archive-quality medical records, and can also be used in telemedicine cervical cancer diagnosis.
The assessment algorithms of the present invention are first applied to low resolution raw images sampled from the live video data stream of a digital colposcope in order to determine when requirements of proper contrast and composition are satisfied. System adjustments are made as needed in response to the feedback from the assessment algorithms. These adjustments may consist of both automatic system adjustments, and manual adjustments made by the operator under instrument guidance. After any adjustments, the assessment algorithms are repeated. After the algorithms indicate that no further adjustments to the system are required, the system is ready to collect high-resolution still images for use in a CAD system.
While many of the assessment algorithms are well-known in the art, the inventors are not aware of any other image processing method that uses a grid box sampling method to estimate the target spectrum that is used by a spectral matched filter to locate a region of interest. The following patents and patent applications may be considered relevant to the field of the present invention:
PCT Application No. WO/2008/012813 to Gal, incorporated herein by reference, discloses a medical device for performing a vaginal examination that comprises an imaging sensor, wide field of view optics, illumination means, electronic circuitry, and communication means. In addition it discloses a medical image and analysis (MIUA) unit comprising a processor and a dedicated MIUA algorithm. The imaging sensor, optics and illumination means gather images at different wavelengths to provide multi-spectral imaging. The imaging device consists of at least one filter. The MIUA algorithm checks the images for the presence of a region of interest and compares the acquired images to a predefined standard of quality and if the acquired images do not meet the predefined standard, adjustments to the illumination intensity, exposure time, angle, and camera zoom can be adjusted. Lastly, the MIUA algorithm verifies that sufficient images of a predefined region of interest have been obtained, and saved, and then signals the user of the same.
U.S. Patent Application Publication No. 2007/0133852 to Collins, Jeffery et al., incorporated herein by reference, discloses a system and method of computer aided analysis of medical images and detection of malignant lesions. Medical images are obtained from multiple modalities and analyzed. Morphological features as well as temporal, i.e., kinetics features, are combined to compute a consolidated assessment of a possible lesion detected in the medical images. The system includes at least one kinetics module, which is capable of extracting kinetics features from a time sequence of MRI images or MRS data taken after administering a contrast enhancement agent to a patient. The consolidated assessment is presented to a user for confirmation or modification.
U.S. Pat. No. 6,766,184 to Utzinger et al., incorporated herein by reference, discloses methods and apparatus for generating multi-spectral images of tissue. The multi-spectral images may be used as a diagnostic tool for conditions such as cervical cancer detection and diagnosis. Primary radiation is produced with an illumination source which is filtered to select a first wavelength and a first polarization. Tissue is illuminated with the filtered primary radiation to generate secondary radiation, which is filtered to select a second wavelength and a second polarization. The filtered secondary radiation is collected with a detector, and a plurality of multi-spectral images of the tissue is generated according to different combinations of first and second wavelengths and first and second polarization with an analysis unit in operable relation with the detector.
U.S. Patent Application Publication No. 2004/0068167 to Hsieh et. al., incorporated herein by reference, discloses a method and system for generating and processing image data based on analysis of an initial image by a computer aided diagnosis algorithm. The CAD algorithm may include modules such as accessing image data, segmenting data or images, feature selection or extraction, classification, training, and visualization. It discloses locating a feature of interest via segmentation or structure identification. It also discloses post-processing techniques that focus on various parameters such as contrast, spatial resolution (e.g. zoom), and color.
U.S. Pat. No. 6,687,329 to Hsieh et al., incorporated herein by reference, discloses a technique for acquiring subsequent image data in a medical diagnostic context based upon analysis of initial image data via a computer aided diagnosis algorithm to determine whether additional image data acquisition is appropriate.
U.S. Patent Application Publication No. 2004/0208385 to Jiang, incorporated herein by reference, discloses methods of enhancing images of tissue samples for diagnostic purposes by filtering luminance values from an input image and transforming the filtered value to produce an enhanced image. The invention uses a transformation algorithm that adjusts for image brightness, contrast, and may provide color balancing. It also discloses a masking technique for regions of a sample that are obstructed or lie outside of a zone of diagnostic interest.
U.S. Pat. No. 6,277,067 to Blair, incorporated herein by reference, discloses a low cost, hand-held colposcopy assembly capable of producing a digital image of the cervix and enables real-time imaging and archiving of cervical images for detecting cancerous tissue. The digital images created may be instantaneously processed to remove reflective glare or to perform any digital image enhancement operations to determine tissue texture, tissue and lesion borders, and tissue vascularity.
U.S. Patent Application Publication No. 2007/0171363 to Chen, Ying-Ling Ann et al., incorporated herein by reference, discloses an adaptive photoscreening system.
U.S. Patent Application Publication No. 2007/0009096 to Cresens and Marc, incorporated herein by reference, a method for canceling the impact of the physical property variability on the image quality performance of a digital imaging system, obtained during quality control (QC) analysis using a serial numbered quality control (QC) target by applying physical property deviation controlled behavior model corrections to the raw image quality performance. The serial numbered QC-target used for the QC analysis comprises target-specific, measured physical property data encoded in- or outside of QC-target.
U.S. Patent Application Publication No. 2007/0237308 to Reiner and Bruce, incorporated herein by reference, discloses a quality assurance system and method that generates a quality assurance (QA) scorecard for technologists that use digital devices in a radiological-based medical imaging study.
U.S. Patent Application Publication No. 2007/0248210 to Selse, Emil et al., incorporated herein by reference, discloses automated quality assessment of a digital mammographic image with respect to the positioning of a patient's breast.
U.S. Pat. No. 6,147,705 to Krauter et al., incorporated herein by reference, discloses an apparatus and method for video colposcope with electronic green filter. A video camera obtains a subject electronic image of a subject object, and using algorithm-driven digital signal processing circuitry (DSP), color saturation, hue, and intensity levels of the subject electronic image are modified according to DSP reference filter algorithm and reference color balance levels as stored, thus producing a modified electronic image corresponding to the subject electronic image. The modified electronic image is outputted to a display in continuous real time as the corresponding subject image is obtained by the video camera. This modified electronic image emulates that obtained through an optical green filter and incorporates a simulated white balance.
U.S. Pat. No. 5,565,678 to Manian, incorporated herein by reference, discloses a system and method for performing a rapid, automatic, quantitative assessment of the image quality of a radiographic image.